Placement of pipes in the ground

ABSTRACT

The invention provides that an underground through borehole (28) is formed with a reaming tool (24). It is filled with a viscous fluid and as soon as possible after being so filled, a flexible lining tube (32) is inserted into the borehole (28) to keep the surface from collapsing until a rigid service pipe (12) has been pulled or pushed into the borehole.

This invention relates to the placement of pipes in the ground.

The said pipes are rigid in nature so as to be capable of supporting theloading applied thereto by the surrounding ground and water table.Typically the pipes will be of steel or other rigid metal.

When it is required to place such pipes in the ground, obviously thereneeds to be excavation or boring in order to provide a cavity to receivethe pipe. The most usual method of placing such a pipe is to use aboring or drilling rig which comprises a reaming head or more usually aplurality of reaming heads and a drill string. The reaming head isdirected by remote control along a particular drilling path under theground. It enters the ground at a shallow angle and then travels alongthe path in which the pipe is to be laid, and it eventually emerges fromthe ground at a desired remote location. A plurality of reaming heads ofincreasing size are used, and the heads are passed sequentially throughthe bore hole. The reaming heads as appropriate may be pulled rearwardsthrough the previously formed borehole, but in any event the hole iscontinually increased in size until it is of the required diameter toreceive the pipe which is simply pulled into position. During thereaming operation, a relatively viscous liquid known as Bentonite isflooded into the borehole being created which serves to some extent tomaintain the shape of the hole and to stop debris and chippings fromcollecting to too great an extent in the base of the hole, and also toassist in the cutting operation, but as can be expected rock chippingsand stones become suspended in the Bentonite, and some do collect at thebase of the borehole. The result of this is that when the rigid pipe iseventually pulled into position it can be obstructed by these loosematerials and if it is obstructed to too great an extent, then it isextremely difficult to pull the pipe into the desired position due tothe friction forces created by these materials. Indeed, in practice itis the case that the length of pipe which can be pulled into a boreholeis limited by these friction forces.

The rigid pipe may typically be a pipe for carrying fluid, or it may bea pipe for carrying other pipes some of which may be fluid pipes andothers of which may be service pipes carrying electrical cables ortelephone cables. Indeed the pipe can itself carry electrical cables.

The present invention seeks to enhance the laying operation to enablethe pipe to be inserted more easily and to enable longer lengths of thepipe to be installed without difficulty.

In accordance with the present invention, in a boring operation whereina rigid pipe is placed in the borehole, wherein a support lining tube ofa flexible nature is used to support the surface of the borehole by theuse of fluid pressure which urges the lining tube against said surface,and the rigid pipe is inserted into the flexible lining tube, andwherein the flexible lining tube is everted into and along the boreholeimmediately behind the last reaming head used for boring the boreholeand wherein the rigid pipe is connected to the trailing end of theflexible lining tube so as to be pulled into the borehole thereby.

In accordance with a further embodiment of the present invention, in aboring operation wherein a rigid pipe is placed in the borehole, whereina support lining tube of a flexible nature is used to support thesurface of the borehole by the use of fluid pressure which urges thelining tube against the surface, and the rigid pipe is inserted into theflexible lining tube, and wherein the flexible lining tube is evertedinto and along the borehole immediately behind a reaming head used forboring the borehole and wherein a pull rope is attached to the trailingend of the lining tube so as to be pulled thereby into the borehole, andsubsequently, the rope is used for pulling the rigid pipe into theborehole.

Preferably, water is used for the urging of the lining tube onto theborehole surface so that the rigid pipe is pulled into the inflatingwater.

By the use of a lining tube, which is pressurized, the chippings andcuttings formed by the reaming operation are kept urged on the boreholesurface, especially if the eversion takes place immediately behind thereaming head.

The everting face of the lining tube will also divert any Bentoniteremaining in the borehole.

The lining tube may comprise a tube formed from a laminate made of afibrous felt material such as a needle polyester felt one side of whichis coated with an impermeable membrane, the laminate being formed intotubular configuration with the butting edges secured and sealedtogether, or it may comprise a fabric which is coated with a syntheticplastic resin so that it is strong enough to withstand the evertingpressure. It is possible to apply the lining tube after the last reaminghead is removed from the borehole, but this would mean that there willbe a significant time period during which the borehole is full of theBentonite and chippings, which would have to be displaced by theinsertion of the lining tube which may cause problems.

The lining tube may be made up of inner and outer sections, and theouter section may be pulled into the borehole behind the reaming head,and the inner section may be everted into the outer section after it isplaced in position.

An embodiment of the invention will now be described, by way of example,with reference to the accompanying diagrammatic drawings, wherein: FIG.1 shows how a borehole is formed in the ground, such borehole being forreceipt of a rigid pipe; FIG. 2 shows a later stage of the boringprocess; and FIG. 3 shows how the lining tube and the rigid pipe areplaced in the borehole in accordance with the preferred method of theinvention.

Referring to the drawing, reference (10) indicates the ground level, andunder the portion of ground shown there is provided an undergroundborehole in which is to be inserted a steel or other rigid pipe (12)(FIG. 3) which may be a fluid carrying pipe such as a water or gas pipe,or may be for carrying service pipes and cables.

In the figures, different sections of the ground (10) are shown becauseone must remember that this borehole to be provided in the ground willbe of substantial length. The borehole is inclined at the respectiveends thereof to a level at which the pipe will be installed.

In the formation of these boreholes, typically a drilling string is usedcomprising a reaming head (14) which is propelled by a rod or drillstring (16) so that an initial borehole (18) is formed.

Progressively, larger reaming heads (20) are passed through thepreviously formed borehole (18) to form larger bores (22).

The process is repeated as many times as necessary, and the reamer maybe entered from either end of the bore hole and it may be pushed throughforwardly or pulled through in reverse.

In the normal method, after the largest reamer (24) (FIG. 3) has passedthrough the borehole creating the final size, the pipe (12) is pushedinto the formed borehole to take its final position.

During the reaming operation, there issues from the drill string,typically the reaming head, a flow of a liquid support material which isa highly viscous liquid known by the name Bentonite. The Bentonite tendsto maintain the integrity of the formed borehole, and also keepsparticles and chippings from falling into the formed borehole. TheBentonite is effective only to a limited extent however, and particlesdo become suspended in the Bentonite or fall to the base of the boreholeas shown at (26) in FIG. 2.

The result of this is that when the pipe (12) is finally pushed into thebore behind the largest reamer (24), the pipe does tend to catch on thechippings and debris in the bore and this makes forcing of the pipethrough the bore difficult. Indeed this has a limiting effect on thelength of pipe which can be inserted into the bore and therefore has alimiting effect on the length of bore which can be provided.

Obviously, it is desirable to be able to make the borehole as long aspossible so that a maximum length of pipe can be inserted, and thisinvention is concerned with a method whereby the insertion of extendedlengths of pipe can be performed without difficulty.

In accordance with the invention a flexible lining tube (32) is appliedto the borehole (28) when it is at its final size prior to the insertionof the tube (12).

As shown in FIG. 3, the borehole (28) behind the final reaming head (24)which is being removed as indicated by arrow (30), is lined by evertinga flexible lining tube (32) into the borehole (28), eversion beingperformed typically by means of water filling the tube in the region(34) and performing the eversion.

To the end of the lining tube (34) the pipe (12) may be attached so thatit is pulled into the borehole by the everting lining tube.

The lining tube (32) keeps the loose chippings and debris from the wallof the borehole in position at the borehole surface, so the resultingsurface through which the pipe (12) can pass is much more smooth and ismore regular.

The lining tube (32) may be constructed of any suitable material. Forexample it may be a tube of fibrous felt material having on its innersurface a coating of impermeable material. By everting such a lininginto the borehole (28) the felt will eventually lie to the inside, andthe film will lie to the outside of the borehole.

In another arrangement, the tube in flattened form may be pulled intothe borehole (28) behind the reaming head (24), and the lining tube maybe inflated by another tube which is everted into the first mentionedtube.

Eversion of felt tubes with coatings is known in lining processeswherein the felt material is soaked with curable synthetic resin. Suchtubes may be used in this method, but of course it is not necessary andindeed it is undesirable that curable synthetic resin should beprovided. The felt tube will in fact be dry.

The lining tube (32) performs only a temporary holding function, becauseafter the rigid pipe (12) has been inserted, the function of the tube(32) is to a large extent terminated. If the ground subsequentlysubsides therefore around the pipe (12), this will be of no significancebecause the rigidity of the pipe is inherent in the material used forsame which typically will be steel or other metal, although othermaterials can be used.

The invention provides an extremely effective means of ensuring thatlong lines of rigid pipe can be inserted in underground bores.

In a modified form of the invention, instead of the pipe (12) beingpulled into the borehole (28) by means of the everting tube (32) astrong rope, e.g. nylon, may be pulled through the borehole (28) by thelining tube or other means, and the rope then is used to pull the pipe(12) into position in the borehole (28). This modification is ofparticular use when the material of the lining tube (32) may not be ofsufficient tensile strength to pull the pipe (12) into position.

I claim:
 1. A method of placing a substantially rigid pipe (12) in aborehole, in the ground, comprising:boring a longitudinal borehole inthe ground with a boring member including a reaming head (24); evertinga flexible lining tube (32) into and along the borehole (28) immediatelybehind the advancing boring member; and supporting the lining tube 32against the surface of the borehole (28) by fluid pressure; connecting asubstantially rigid replacement pipe (12) to the trailing end of aflexible lining tube (32), the rigid pipe (12) is pulled into theborehole (28) as the flexible lining tube (32) everted by fluidpressure.
 2. The method of lining a borehole of claim 1, including thestep of attaching a pull rope to the trailing end of the lining tube(32) and attaching the opposite end of the rope to the leading end ofthe substantially rigid pipe (12) so that the pipe is pulled into theborehole (28) as the flexible lining tube (32) is everted.
 3. The methodof claim 1, including the step of filling the borehole (28) with aviscous fluid before everting the lining tube (32) into the borehole(28).
 4. The method of claim 1, including selecting a lining tube (32)which is a laminate of a layer of fibrous material and a plasticmaterial film or a coating on at least one surface of the felt, arrangedso that after eversion the the film or coating is disposed on the insideof the tube (32).
 5. The method of claim 1, including the step ofselecting a lining tube (32) of a first section and a second sectionattached to the first section;pulling the first section into theborehole (28) and the second section is everted into the outer section,the substantially rigid pipe attached to the trailing end of theeverting second section to pull the rigid pipe (12) into the borehole(28).
 6. A method of placing a substantially rigid pipe (12) in aborehole (28); comprising:boring a longitudinal borehole in the groundwith a boring member including a reaming head (24); everting theflexible lining tube (32) with a fluid immediately behind the advancingboring member (24); supporting the flexible lining tube (32) against thesurface of the borehole (28) by fluid pressure; attaching a pull rope tothe trailing end of the everting lining tube so as to be pulled into theborehole (28); and attaching the trailing end of the rope to thesubstantially rigid pipe (12) for pulling the pipe (12) into theborehole (28).